Before a noun with no determiner, we use all without of.
All children need love. (NOT All of children need love.) Link
I don't understand why All of children is not correct.
Could you explain logically or semantically why it does not make sense?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
**(All of children need love.)****
You are allowed to use all and all of before nouns and before this and that. However, if the noun is used without an article, possessive or determiner then all of is not used.
If we add a definite article to your sentence then we can use all of.
e.g. All of the children need love. (the is used if you are speaking about a specific group of children).
These are the rules. Why they are this way is not possible to say. It's just the way the language is. (as far as I know).
 All children need love.
* All [of children] need love.
All is fine in  where "all" functions straightforwardly as determiner of "children".
In  The presence of "of" marks it as a partitive construction. Partitive noun phrases like the one in brackets must be marked as definite by a definite determiner such as "the", but it is missing here and hence the sentence is ungrammatical. If "the" or another definite determiner is inserted all is well:
All of the/these/those children need love.
Your guess is as good as mine on any logical explanation for this one. To further complicate matters, although you can only use "all of" with articles and pronouns, you can still omit the "of" when you do use articles.
That is, both of the following are correct, and if there is any difference between them, I can't tell you what it is:
All of the children
All the children
These are both also correct:
All of those children
All those children
The "of" is still obligatory with pronouns. You can't say "all them." You must say "all of them."
I can't think of any way to really make sense of this. It's mystifying! But unless it's in front of an objective pronoun, you usually will be okay if you just always say "all" instead of "all of."